Cranes are widely applied as lifting and conveying equipments in construction industry, manufacturing industry, and port transportation industry. There are various kinds of cranes, each kind of which is of a different structure. For a truck crane, it includes a chassis, a slewing mechanism, a lifting arm, a hook and a hoisting mechanism. The lifting arm has a lower part connected with the chassis by the slewing mechanism and an upper part on which the hook is hung by a wire rope wound around a pulley block to be connected to the hoisting mechanism. In the hoisting mechanism, the hook is driven by the wire rope to make movements such as rising, stop and lowering; while the lifting arm may rotate about a vertical axis under the driving of the slewing mechanism, so as to move the hook in a horizontal plane.
In the hoisting operation of a crane, there are many steps to be performed, which generally include lowering a hook, hoisting, laterally moving and subsequently lowering the hook, etc. In lowering of the hook, a hoisting drum of the hoisting mechanism rotates in one direction, and the hook brings the wire rope to move downwardly under gravity, till the hook reaches a suitable position above the goods to be hoisted, and then the hook is fixed to the goods to be hoisted. In hoisting, the hoisting drum of the hoisting mechanism rotates in an opposite direction, and the hook and the goods are moved together upwardly by the pulling of the wire rope, thus the goods goes away from the ground. After the goods has been moved away from the ground, the slewing mechanism is operated and the step of the laterally moving begins. The lifting arm laterally rotates, and the hook laterally moves together with the goods, so as to allow the goods to arrive above a predetermined position. In subsequently lowering of the hook, the hoisting drum rotates reversely again after the goods arrives above the predetermined position, and the goods and the hook moves downwardly, so as to allow the goods to reach the predetermined position, thereby performing the transposition of the goods. In hoisting, the hook moves not only in a vertical direction but also in a lateral direction. Due to inertia and an external force, the hook hung on the upper part of the lifting arm by a wire rope and the goods may sway accordingly, in particular when the hook carrying the goods begins to move laterally or stops laterally moving after the goods reaches the predetermined position, the swaying amplitude of the hook and the goods may be increased.
The swaying of the hook may affect the efficiency of the hoisting operation of the crane. When the hook is lowered, in order to keep the hook stable relative to the goods and avoid the collision between the hook and the goods, it is necessary to wait for a suitable period of time, until the hook stops swaying. In the laterally moving of the hoisted goods, in order to avoid the collision caused by swaying of the goods, it is also necessary to move the hook and the goods at a relatively low speed. After the hoisted goods reaches the predetermined position, in order to accurately place the goods onto the predetermined position, it is also necessary to lower the hook after the goods stops swaying. Currently, in the filed of crane, there is a common problem that the hoisting time is prolonged due to the swaying of the hook, which reduces the hoisting efficiency of the crane.
The above-mentioned problems occur not only in the hoisting operation of a truck crane, but also in the hoisting operation of a gantry crane or other types of cranes.
In view of the above-mentioned problems, the swaying amplitude of the hook is currently reduced by taking a anti-swaying hook-stabilizing measures, so as to more quickly stop the swaying of the hook and thus to reduce the adverse effects of swaying hook on the efficiency of the hoisting operation. In the anti-swaying hook-stabilizing measures, a control device is generally used to move the hook at a suitable frequency and amplitude in the direction opposite to the swaying direction, based on the swaying amplitude, frequency and direction of the hook, so as to stop the hook in a shorter time. Presently, the anti-swaying hook-stabilizing measures substantially depend on the appropriate control on the hook by experienced operator.
In order to reduce the dependence on the operating experience of the operator, the European patent document EP1757554 disclosed an anti-swaying control technique for a crane. In the technical solution disclosed in this patent document, attitude parameters of a hook or goods are predetermined in a preset mode, and a control system takes a proper anti-swaying measures according to the predetermined attitude parameters to reduce the adverse effects of swaying on the hoisting operation. One principle of this technical solution is that the movement situation of a hook, i.e., attitude parameters of the hook, in hoisting operation is predetermined; and a control strategy is determined according to the predetermined attitude parameters of the hook to allow the hook move in a predetermined way, so as to reduce the swaying amplitude of the hook and thus to stop the hook more quickly, thereby reducing the adverse effects of the swaying hook on the efficiency of the hoisting operation. However, due to the complexity of the actual hoisting operation, it is difficult for the predetermined attitude parameters of the hook to be identical with the actual attitude parameters, thus this technical solution is only applicable in a stable hoisting operation environment. When a hoisting operation is performed in an operation environment where the attitude parameters of a hook are not predetermined, the above technical solution will not increase the efficiency of the hoisting operation of the crane.
In a hoisting operation, one technical difficulty in the crane field is to determine the actual attitude parameters of a hook and provide a basis for controlling the movement of the hook so as to increase the efficiency of the hoisting operation of a crane.